Ratpoison is a tiling window manager that allows the user to manage applications without a mouse. The user interface is inspired by GNU Screen. It comes with a small set of default keybindings, which are all initiated by Ctrl-t. Configuration is done in ~/.ratpoisonrc. Note that you can't use the mouse to focus windows. This makes it somewhat unusual to use.
The most important default keybindigs are:
Website: https://www.nongnu.org/ratpoison/